1. Field of the Invention
The invention relates to a method for producing a rotor blade for a wind power plant, which has a drainage bore hole in the area of the rotor blade tip, a rotor blade for a wind power plant with a drainage bore hole in the area of the rotor blade tip, a wind power plant with a corresponding rotor blade and the use of a surface element in a rotor blade for a wind power plant, which has a drainage bore hole in the area of the rotor blade tip.
2. Description of Related Art
Water collects inside rotor blades of wind power plants as a result of condensation or direct penetration and must be drained. If the water cannot escape, there is a risk in the winter that the water freezes and the rotor blade can be damaged or destroyed through expansion during freezing. Another potential risk is that the accumulated water in the rotor blade tip vaporizes abruptly as a result of a lightning strike into the rotor blade tip, whereby the rotor blade can also be damaged or destroyed. Thus, rotor blades for wind power plants are provided with a drainage bore hole in the area of the rotor blade tip that connects the inner side of the rotor blade with its outside and makes it possible for the water to escape.
EP 1 342 009 B1 discloses a rotor blade for wind power plants, which has a lightning rod in the area of the rotor blade tip, which is arranged in a bore hole in the blade tip. Lightning rod and bore hole together form a drainage system for the rotor blade.
DE 10 2004 028 917 A1 discloses a rotor blade for a wind power plant, which has at least one hollow space, which is adjacent to an outside of the rotor blade and is connected with the outside via at least one drainage bore hole. A water-permeable collection element, such as a sieve, is arranged in the hollow area such that water gets to the drainage bore hole from the hollow space through the collection element. It is, thus, prevented that the drainage bore hole gets clogged with dirt and small particles after some time, which are also present inside the rotor blade and can be rinsed with water through the drainage bore hole.
The rotor blade tips described in these documents are very complicated to manufacture since they have the drainage bore holes on the outermost blade tip so that a very exact form fit and manufacture is necessary at this location. In the case of a construction method of a rotor blade with half shells or with corresponding molded parts, a corresponding drainage bore hole, which is arranged in a joint to be glued between the half shells, also forms a structural weak point in the joint such that the rotor blade is structurally weakened on the rotor blade tip.
Alternatively, a drainage bore hole can also be provided in the area of the rotor blade tip on the suction side or the pressure side of the rotor blade. The leading edge of a rotor blade is connected with the trailing edge of the rotor blade via the suction side and the pressure side. The suction side of the rotor blade is the side with the longer flow surface with respect to the pressure side.
Even when a drainage bore hole is arranged in the area of the rotor blade tip on the suction or pressure side of a rotor blade, the water is pushed out of the inside of the rotor blade through the drainage opening through the effects of centrifugal force when the rotor is rotating.
Another effect, which supports drainage, is that water is suctioned out of the inside of the rotor blade through the drainage bore hole due to the low air pressure of the air flowing past the suction side at a high speed according to Bernoulli's principle. The rotor blade is not normally hermetically sealed on its blade root so that an air flow can be created due to this effect. This effect also occurs to a somewhat lesser degree on the pressure side of the rotor blade so that a suction bore hole can also be arranged on the pressure side of a rotor blade.
One difficulty with the production of a drainage bore hole on the suction or pressure side of the rotor blade in the area of the rotor blade tip is that rotor blades are generally made of half shells, i.e. molded parts, which represent the suction side or respectively the pressure side, that are glued together.
In larger wind power plants, corresponding molded parts are generally made of fiber glass and/or carbon fibers in fiber-composite technology and are connected with synthetic resins such as polyester resins or epoxy resins. The half shells can also be made of several molded parts respectively for the pressure side and for the suction side, which also must be connected with each other.
In order to establish a secure connection, the molded parts of the pressure side are generally glued to the molded parts of the suction side. Suitable connection means are in particular adhesives or adhesive mixtures, for example made of polyester resins and/or epoxy resins. In particular, in the area of the rotor blade tip, a large amount of adhesive is needed for this.
Since the connection means when gluing the molded parts together is liquid and an adhesive excess is unavoidable in order to guarantee a secure adhesion, the connection means can run uncontrolled into the inside of the rotor blade. However, since the adhesive expansion inside the blade occurs uncontrolled, it is not possible to always place a drainage bore hole at the same location since this location can be covered by connection means. However, if the drainage bore hole is always bored at a sufficient distance from the blade tip, then a considerable amount of water can collect inside the blade under certain circumstances.